(CNN) -- China's foreign minister has promised Washington that Beijing would push North Korea to return to six-party talks over its nuclear ambitions, a senior U.S. State Department official said.

The promise was made in a phone call between U.S. Secretary of State Condoleezza Rice and China Foreign Minister Li Zhaoxing, the official said.

China's Xinhua news agency reported that Zhaoxing told Rice he would stay in touch with the Pyongyang government and the other parties to the talks.

The talks have taken on a greater sense of urgency after North Korea admitted publicly for the first time last week that it possessed nuclear weapons.

Previously it had asserted its ability and right to produce them.

In April 2003, U.S. officials said that North Koreans claimed in private meetings they had at least one nuclear bomb.

Rice meets Monday with South Korean Foreign Minister Ban Ki-Moon, who told CNN's "Late Edition with Wolf Blitzer" the six-party talks should continue, and that North Korea must abandon its nuclear weapons program.

Since 2003, the United States, the two Koreas, China, Japan and Russia have held three rounds of talks aimed at persuading the North to abandon its nuclear weapons development in return for economic and diplomatic rewards.

But no significant progress was reported in those talks, all hosted by China.

A fourth round of talks in September did not take place when North Korea refused to attend, citing what it called a "hostile" U.S. policy.

Last week Pyongyang said it would not return to the talks.

In the past Pyongyang has insisted on one-to-one talks with the United States, but Washington says a multilateral diplomatic approach is required, a call echoed by South Korea.

"Nuclear issues should be resolved in close cooperation of the international community," Ban said.

"We do not see nuclear issues as bilateral issues."

World leaders expressed concern last week after hearing that North Korea would quit the talks and "bolster its nuclear weapons arsenal."

Thursday's statement from the North Korean Foreign Ministry said nuclear weapons are "for self-defense to cope with the Bush administration's evermore undisguised policy to isolate and stifle" its government.

The communist state said it felt "compelled to suspend" participation in the six-nation talks "for an indefinite period."

U.S. diplomats have said that North Korea has used similar language when stepping aside from anti-nuclear proliferation talks in the past.

But it is the first time Pyongyang has been so explicit about developing nuclear weapons.

Rice has said that Pyongyang is risking further isolation "because everyone in the international community, and most especially North Korea's neighbors, have been very clear that there needs to be no nuclear weapons on the Korean Peninsula in order to maintain stability in that region." (Full story)

Some observers in Washington say Pyongyang may be posturing for a more preferable negotiating position in light of recent developments regarding the suspected nuclear program in Iran. (Full story)

Russia's Foreign Ministry said it regretted North Korea's decision.

In a statement on the ministry's Web site, spokesman Alexander Yakovenko said Moscow is "carefully studying" the announcement and added, "For us it can only cause regret ... to our mind, this attitude contradicts Pyongyang's declared striving for denuclearization of the Korean Peninsula.

U.N. Secretary-General Kofi Annan said North Korea could be brought back to the negotiating table. British Foreign Secretary Jack Straw agreed, saying, "It would be a major mistake by [North Korea] were they to go down this route."

Bush tones down 'axis of evil' rhetoric

In his February 2 State of the Union address, U.S. President George W. Bush only briefly mentioned Pyongyang, saying Washington was "working closely with governments in Asia to convince North Korea to abandon its nuclear ambitions."

Bush's tone was in stark contrast to his speech three years ago when he branded North Korea part of an "axis of evil" that included Iran and Iraq. This year's address raised hopes for a positive response from North Korea.

Earlier this month, Bush and South Korean President Roh Moo-hyun agreed to push for an early resumption of the six-nation talks.

But Pyongyang said Bush's call for the spread of freedom in his inaugural speech was a diabolical scheme to turn the world into "a sea of war flames."

"In his inauguration speech, Bush trumpeted that 'fire of freedom will reach dark corners of the world.' This is nothing but a plot to engulf the whole world in a sea of war flames and rule it by imposing a freedom based on power," North Korea's state-run Pyongyang Radio said this month.